Eddy-current apparatus



Jan. 16, 1945. M. P. WINTHER EDDY-CURRENT APPARATUS Filed June 17, 1943 5 Sheets-Sheet 1 Jan. 16, 1945. M. P. WINTHER 2,367,636

EbDY-CURRENT APPARATUS Filed June 1'7, 1945 5 Sheets-Sheet 2 Jan. 16, 1945. w l- 2,367,636

EDDY- CURRENT APPARATUS Filed June 17, 1943 5 Sheets-Sheet 3 Jan. 16, 1945. WINTHER EDDY-CURRENT APPARATUS 5 Sheets-Sheet 4 Fils-zd June 17, 1945 Jan. 16, 1945. M. P. WINTHER EDDY-CURRENT APPARATUS Filed June 1'7, 1945 5 Sheets-Sheet 5 Patented Jan. 16,1945

EDDY-CURRENT APPARATUS Martin P. Winther, Waukegan, 111., asslgnor to Martin P. Winther, as trustee Application June 17, 1943, Serial No. 491,101

29 Claims.

This invention relates to dynamometers and the like, and with regard to certain more specific features, to water-cooled, eddy-current dynamometers.

Among the several objects of the invention may be noted the provision of a smoothly operating eddy-current dynamometer having a water-cooled flux gap in which water surging effects are practically entirely eliminated; the provision of a dynamometer of the class described in which water cooling of the gap is so carried out and augmented by water cooling behind the eddy-current surfaces, that the efficiency of cooling is increased, and thus not only increasing capacity but also reducing stresses and distortion in the rotary eddy-current member; the provision of a dynamometer of the class described which is adaptable to large capacities and a wide range of speeds without sacrifice of operating steadiness, sensitivity or accuracy of power measurement; and the provision of apparatus of this class which is fundamentally simple in construction and operation. Other objects will be in part obvious and in part pointed out hereinafter.

The invention accordingly comprises the elements and combinations of elements, features of construction, and arrangements of parts which will be exemplified in the structures hereinafter described, and the scope of the application of which will be indicated in the following claims.

In the accompanying drawings, in which is illustrated one of various possible embodiments of the invention,

Fig. 1 is a longitudinal section on a much reduced scale of a 3500 horsepower machine embodying my invention;

Fig. 2 is a right-end elevation of Fig. 1;

Fig. 3 is an end view of one of three toothed intermediate rings, the view showing at the top in dotted lines the positions of three teeth on the next ring and also showing the relative locations of certain holding bolts;

Fig. 4 is an enlarged fragmentary detail View showing the inside arrangement of the three adjacent intermediate rings, being viewed substantially from line 4-4 of Fig. 3;

Fig. 5 is an enlarged longitudinal section taken on line5-5 of Fig. 4, line 5-5 of Fig. 3 indicating what would be the position of the section on that figure;

Fig. 6 is an enlarged view enlarged in scale over the other drawings of a special polar tooth of Fig. 3, the tooth being for application of a temperature alarm and theiview being viewed from line 6--6 of Fig. 3;

Fig. 7 is an enlarged longitudinal section of the temperature alarm mechanism, the view being located substantially on line 1-4 of Fig. 6;

Fig. 8 is a detailed view (also enlarged in scale) of an inspection hole, the view being taken substantially on either of lines 88 of Fig. 3;

Fig. 9 is a longitudinal section taken on line 9-9 of Fig. 3 and showing a, drainage passage;

Fig. 10 is a graph of the operation of the present machine compared to a graph of operation of certain former machines;

Fig. 11 is a view similar to Fig. 3 but showing an end ring and being on a reduced scale; and,

Fig. 12 is a view similar to Fig. 3 but showing a center ring on a reduced scale.

Similar reference characters indicate corresponding parts throughout the several views of the drawings.

This invention is an improvement upon the construction shown in the mesne assignee's United States patent application of Charles T. Hayes, Serial No. 477,817, filed March 3, 1943, now Patent No. 2,351,963, dated June 20, 1944; and upon United States Patent 2,188,398, issued to Ernest Bernard, dated January 30, 1940.

Theoretically, water cooling the flux gap of an electrical dynamometer is ideal, but in practice the introduction of water into the gap, if not properly managed, causes the dynamometers to partake of some of the undesirable characteristics of hydraulic dynamometers. That is to say, churning of the water tends to set up so-called surging or stuttering" efiects which make it very diflicult to maintain a steady balance on the dynamometer weight scales, and readings on the scale are often therefore diflicult and sometimes impossible to obtain accurately. This is particularly true in machines of high capacity. In addition, high capacity machines are much more subject than others to troubles from stress distortion of the rotor due to localized uneven heating.

Attempts to eliminate the above difllculties should, if possible, not introduce more complexities than were heretofore inherent, because in large sized apparatus these increase the cost of construction and maintenance to prohibitive figures. The present invention at practicable cost produces a high capacity machine which operates very smoothly so that steady readings can be obtained for accurate calculation of large torque.

Referring now more particularly to Fig. 1, there are shown at numerals I supportin pedestals carrying bearings 8 for a rocking stator indicated generally at S. Broadly this stator 8 consists of end closing members 1 bolted to what will hereinafter be referred to generally as an internally toothed water-tight stator cylinder 9, preferably composed of dynamo steel or similar magnetic material. The details of this cylinder will be described later.

The end members 1 have bolted thereto hoilow end gudgeons II which rock in the bearings I. The same bolts which hold the gudgeons ii in place also hold to the end members 1 plain cylindric bearings II. The bearings 13 support a rotary drive shaft 15 which passes through oil seals 11 in the end members 1 of the stator S. This shaft l5, inside of the seals I1, is keyed to hubs ll of an eddy-current rotor R. The prime mover to be tested drives shaft 15.

To the hubs I! are bolted rotor heads 2|. Heads II are formed outside with internal annular edgewise grooves 23. These grooves are within lips i1 and by means of openings communicate with the inside of the rotor.

The same bolts which hold the heads 2| to the hubs II also hold the rotary components of labyrinth water seals 21. These are located between the rotor R and the stator S. The stationary components of said labyrinth seals 21 are cut into the insides of the stator heads 1.

Between the hubs l9 and located on shaft 15 is a third hub or supporting spider 29. Between spider 2! and each of the heads 2| is supported a hollow, aylindric eddy-current drum 3| which has a smooth external cylindric surface throughout its length except for slight end tapers. Each drum ii is composed of magnetic material, such as dynamo steel or the like. Each drum II is flanged as shown at I! for bolting to the central spider 29 and is bolted at its other end to the respective head 2|. The eddy-current or armature drums ii are tapered at their ends as indicated at for purposes which will be described. Internally and near their ends, both armature drums are Provided with. internal beads 31 for purposes which will later also be made clear. At their adjacent ends, near the center of the machine, the drums II are perforated as shown at a, thus forming central communications between the inside and the outside or the rotor.

The parts of the composite cylindric part 9 of the stator S will now be described. There are two outer containing cylinders 4| into each of which are fitted a series of intermediate annular rings 43, end rings and center rings 41. Rings 43 are shown in Figs. 1 and 3; rings 45 in Figs. 1 and 11; and rings 41 in Figs. 1 and 12. Rings 45 and 41 are diflerent in detail from rings 43 and from each other to make them attachable to adJacent parts, but basically all perform similar functions. The end rings 45 are bolted respectively to respective ones of the adjacent heads 1 (see bolts-and-holes 45). The center rings 41 are abutted at a tongue-and-groove joint 49, and held by bolts-and-holes 48. They are respectively abutted with the inner ends of the outer cyl-' inders 4|. The intermediate rings 43 are welded together and bolted, as will be shown.

As above indicated, each or the rings 43, 45

and 41 is shown in detail in end view in Figs. 3. 11 and 12 respectively.

Referring to one ring 43 shown in Fig. 3, it

will 'be seen to comprise an annulus or dynamo steel of T-shaped cross section (see also Figs. 4

and 5). The cross of the T is axial, and is hum-- hered ll. Thetrunkof theTis radial'andis indicated at 5!. This produces two lateral grooves 55, each of which. with the adjacent groove in the adjacent ring, provides peripheral space for an annularly wound field coil 51. The flange 55 is tapped at opposite points as indicated at 58 for bolting to the surrounding cylinder 4|. Within each coil 51 the adjacent edges of adjacent rings are grooved at 42 to receive plain sealing rings I which may or may not be ma netic. To have these rings non-magnetic is preferable, but since they are of rather small cross section as indicated, the undesired flux leakage through them, even if they are magnetic, is not appreciable. The rings ii are preferably attached to the adjacent rings 41 by welding, thus forming a water seal to protect the adjacent coil 51.

Internally, the portion 5| of each ring 43 is formed as teeth 53 of novel form. These teeth are formed integrally on the ring. The bases of the teeth are or the same width as the width of the T section 5|. Laterally they flare out, as shown at 65, but peripherally they taper inward, as shown at 51. Their ends are flat as shown at 59. The purpose or this form of tooth is to provide overlap between adjacent bands of teeth, as indicated at 0 in Fig. 4, but at the same time to have a toothed end area 1| which is smaller than the area A--B of the section of the tooth where it joins the ping section 51. The ratio of the end area 1| to the base area A-B is such as to obtain as high a flux concentration as is practicable from the end area H. For example, the base area A-B is approximately 1.3 times the end area 11 which approximately saturates the tooth ends. However, the end areas of the teeth in adjacent rows overlap peripherally. This latter feature results in advantages whichwill appear hereafter. In order to permit of the overlap, teeth of adjacent rings 43 ar angularly phased apart one-half the pitch distance between adjacently located teeth. This is shown for three rings in Fig. 4. Similar principles hold with regard to the teeth of the end rings 45 and 41, although being adapted to their particular endwise positions in which they [form attachments, endwise parts of their teeth are eliminated (see Fig. 1). How the staggered teeth between adjacent rings appear is also indicated by the dotted lines at the top of Fig. 3.

Fig. 12 shows the bolt holes 48 for holding bolts 50 (see also Fig. 2) by means of which the center rings 41 are held together. Fig. 12 also shows spaces 52 in the center rings in which teeth 63 have been skipped to provide for eyes 54. Fig. 11 shows similar spaces 52 in the end rings in which teeth BI have been skipped to provide for another set of eyes 54. The eyes 54 in rings 45 align with the eyes 54 in rings 41. Holding bolts 54 pass through the eyes 54 of each set of rings 45 and 41, being accommodated by spaces 52 also in the intermediate rings (Fig. 3). These hold together between each pair of rings 45 and 41, three intermediate rings 43. The two left and right assemblies of rings thus made are welded and the assemblies then centrally joined as shown at 50 (Figs. 2 and 12) It will be noted that at the top are no internal eyes 54 nor skip spaces 52. At this point longitudinal rods 52 are welded between teeth in order to augment the holding action of the welds between rings.

In order to bring water into the space between the inside of the stator S and the outside of the rotor R (in which space are said teeth 53), each 1 ring is drilled and tapped at the top as indicated at 13 for an inlet pipe 15 which passes.

through a suitable opening in the respective cylinder 4|. In Fig. 1, six such pipes I5 are shown. Each passes through a water inlet manifold and is sealed thereto on the opposite side as indicated at I9. Each pipe 15 has a blind stop 8|. and internal water inlets, as shown at 93. Hence any water under pressure in the manifold 11 enters the space between the stator S and the rotor R via the pipes I5 at spaced points along the cylinder 9. Water entry may be at as many points as there are intermediate rings, as shown, or more or less points of entry may be employed. The amount of water to be introduced will be discussed hereafter.

The manifold I1 is supplied with water through a bank of parallel soft rubber hoses 85 which run from pipes 91 leading from a supply manifold 89 mounted on one of the pedestals I. Water is brought to the machine over pipe 9I. The purpose of using a bank of parallel hoses 85 is flexibility. A plurality of small hoses is more flexible for a given amount of water than a single large hose, and maximum flexibility is desired so that the stator S may rock as freely as possible in the bearings 3. The stator S (on center rings 41) carries suitable pads 93 (Figs. 2 and 12) to which the usual dynamometer arms are applied for transmitting torque to a suitable weighing scale for determining the force value by means of which computations are made for horsepower absorbed by the machine.

As indicated in Fig. 1, each header I is dishshaped, thereby providing an annular passage 95 embracing the adjacent lip 91. At the bottom of the machine, the headers 1 are provided with sumps 99. Pipe connections I9I -join the sumps 99 with a central outlet box I93. Soft rubber hose connections I95 provide for free relative rocking movement between the stator and the stationary box I93. The box is connected by means of pipe I91 with a suction pump I99. Pump I99 supplies a negative discharge pressure through the pipes I9I and the headers I, thus rapidly drawing water out from the ends of the rotor.

At the bottom of each ring 43, 45, 41, as the case may be, as indicated, is a recess III (see also Fig. 9), adjacent recesses being aligned to provide for axial flow of any water that may leak or seep past the joints of the rings 6|. This recess being at the bottom of the machine, such water will find its way axially to an outlet shown at H3 of Fig. 9.

The rather small-scale cross section of Fig. 1 has been ideally taken so as to avoid going through the passage III shown in Fig. 9. This has been done for purposes of maintaining cl'arity, but it will be understood that the leakage channel III connects with opening H3 as shown in Fig. 9. It is to be understood, however, that leakage is not intended, and that ordinarily it will not occur, and that under such circumstances the passage II I has only a potential func: tion.

It should also be understood in connection with Fig. 1 that the teeth 63 are shown in elevation to avoid confusion.

In Figs. 3, 11 and 12 the recesses shown at II! on each ring are for lead-in wiring to the coils 51.

General operation is as follows:

The coils 51 are energized with direct current from a suitable source, thus engendering toric flux fields around the respective coils as exemplified at F in Fig. 1. The current in adjacent coils flows in opposite peripheral directions, so that bucking action between the magnetic circuits between coils is avoided. This is indicated by the arrowheads on the magnetic circuits shown in dotted lines at F. This makes the adjacent bands of teeth 63 of opposite polarities, namely,

north and south as indicated at N and S. Flux" concentrations emanate-from a band of teeth of north polarity, loop through the adjacent drum 3I, then pass into a tooth band of south polarity, thus closing magnetic circuits around the coils 51. Since the drums 3I rotate, being driven from the prime-mover shaft I5, heating eddy currents are engendered in the drums 3I. Water flows through the passages 9|, 89, 81, 85, ll, pipes I5 and into the stator through the openings I3. This places it between the drums 3| and the stator S.

At this point, an important feature should be noted. The amount of water allowed to flow into the machine is less than that which would flll up the space between the rotor and the stator. Where solid bodies of water are permitted to make contact with a revolving drum or disc, it is practically impossible to avoid surges, because the resulting water ring tends to form an imbalance beat effect with the revolving drum. This imbalance beat causes surging at the dynamometer scale and makes accurate measurements almost impossible.

In the present invention, the amount of water introduced is small enough to cause it to strike the drum upon entry and to be flung off promptly, initially absorbing a relatively small amount of heat. The water being centrifugally driven from the drum due to its high surface velocity strikes the inwardly protruding teeth 93. It is then splashed back against the drum, the action being repeated several times before the water picks up suflicient heat to obtain a reasonable discharge temperature. The water picks up several degrees of temperature each time that it impinges upon the drum. There are no solid bodies of water anywhere except at the bottom of the machine where the water drains away from the drum without bodily coming into any (or at most very little) contact with the drum. This splash system cooling of the drums pro- 1 vides a very small drag, and it is constant, which are important features.

It has been found that, if the space in which the armature or rotor drum moves be filled with water so as to immerse the drum over even a substantial fractional part of its periphery in water, the hydraulic drag becomes so great as to take over a large part of the total torque effect required of the machine. This torque effect is subject to all the objectionable instabilities of hydraulic machines, namely inflexibility from a fixed torque and surging. Hence the maintenance of a fine spray feed is of substantial importance.

The longitudinal positions of the teeth 63 act as barriers against spinning action even of the broken-up water.

Thus, since there is no solid body of water permitted to build up against the drum, no surging occurs. By using several impingements of water against the drum, the drum temperature becomes only a few degrees above the water discharge temperature, for example, water will enter at between 40 F. and F. and will discharge at between F. and F. This will produce temperatures in the drum not exceeding 209 F. or so, thus avoiding high fiber stresses in the metal. For instance, if the rotor B. were permitted to operate at 400' I". and the supporting diaphragms II were operating at 100 F. (and they probably would be at lower temperatures), the temperature difference between the drum and the diaphragms would be 300 F. Since these parts are physically tied together, there would be a force exerted between the hot and cold members in proportion to the thermal expansion, and calculations show that such a difference would set up an unsafe fiber stress. This does not occur by use of the present invention.

From the above it is clear that the water wets the rotor surface, but it is mainly spun off against the upper stationary teeth 63 which operate as bames, causing the water to flow back again to the rotor surface. Control of water flow is obtained by proper sizing of the inlets 13, in view of the water pressure available, or with a given size of inlet opening I3 controlling the water volume by suitable valves. Practically, it is only necessary to adjust the amount of water circulating to the point where any undesirable surging is eliminated, which is an indication that there is no substantial contact between any solid mass of water and the rotor. It will be understood that a depth of water such that the rotor is contacted at the bottom for a short arc may be tolerable, provided that any surging effect is of negligible amount. But, in any event, the space between the rotor and the stator is to be far from being filled up with any cylindric volume of water or any substantial fraction of a cylindric volume which will surround the rotor.

The tapered portions at the ends of the drums Ii are to reduce the sections at these The diminished production of heat adiacent the heads II is desirable in order further to lower.

the temperature difference between the hot armature surfaces and the end plates or heads ii. The idea is to obtain as uniform a stress as possible at the drum ends, rather than an abrupt change, thus further minimizing stresses at the peripheries of the heads 2 I.

Some water proceeds all around from between the ends of the rotor and stator and into the rings 1, where it descends, and in doing so strikes the outer periphery III of the labyrinth seal 21. From here it is thrown in behind the inwardly directed flange 91, and thus into the grooves 28 from whence it proceeds through the openings 20 into the drums. Here by centrifugal force it gathers to a film depth equal to a depth of the beads I1. Any excess spills over the inner beads and travels centrifugally out through the openings 38 at the center, then circulates back to the headers I. By this means, some cooling effect is obtained on the rear faces of the eddy-current surfaces.

The peripheral overlap of adjacent bands of staggered teeth SI has been mentioned above. This feature is of substantial consequence in makingdynamometers of very high torque requirements, because it permits the size of the dynamometer to be reduced substantially. The reason is as follows: The portions of the teeth above their bases 13 (Fig. 4) are upwardly tapered down to a smaller end area, and so far as fluxasamas of the armature II, a north pole follows a south pole. This produces a very high torque at low speeds, which is a characteristic of salient-pole machines in which relatively to the eddy-current surface a north pole follows a south pole.' At the same time, the portions of the teeth outside of the overlap O produce relatively to the eddy-current surface a condition in which peripherally a south pole follows a south pole, or a north pole follows a north pole, depending upon which band 01 teeth is under consideration. This avoids the droop in the torque curve at high speed which is characteristic of salient-pole machines, or in other words, it produces a rising torque curve where the action of the salient poles leaves off.

Fig. 10 is a plot making this clear. In this ngure units of torque are plotted against R. P. M. Curve "a" is a normal torque curve of a prior clutch such as shown in Patent 2,106,542, wherein the toothed method of concentrating flux is shown. In that patent it is explained how with an ordinary salient-pole machine the torque curve droops.

concentrating action i concerned, operate along the lines of the teeth or poles described in U. 8. Patent 2,106,542, U. 8. Patent 2,197,990 and U. S. Reissue Patent 20,225. Adjacent bands of these teeth are of north and south polarity as indicated in Fig. 4. The overlapped portions 0 operate differently. That is to say, relative to the periphery Curve b of Fig. 10 shows how the staggered and overlapped teeth such as used herein raise the values of torque, particularly in the low-speed region. In other words, the knee of the-curve is made sharper so that a flatter overall characteristic is obtained.

Stated another way, the toothed improvement of Patent 2,106,542 avoids droop at the highspeed portions of the torque curve at some sacriflce of high torque at low speeds, while the present invention avoids altogether the latter sacri' fice. The former construction was very useful because most operations are at high speed, but the present construction is much more useful over a wider speed range because of the higher torque produced at lower speeds.

Figs. 3, 6, 'I and 8 show certain safety features. They are particularly useful on machines of high capacity where damage due to oversights in watchfulness may be very expensive.

One or more of the teeth 83 may be made up specially as indicated at 63A (Figs. 3, 6 and 7) with a boss m in which an opening m is drilled and tapped to receive the apparatus shown in Fig. 7. This consists of a threaded guide cup I22, held in position by a spanner type lock nut I25. Passing through the cup I2! is a feeler gauge I21 having a flange I28 resting downwardly against a stop III. An upward shoulder member I" forms a reaction pad for an internal spring I" which biases the shoulder I29 downward to its predetermined lowermost position. This position is one in which the end I31 of the sealer just clears the inner ends of the teeth 63 and the outer cylindric surface I39 of the adjacent armature drum II. The upper end III of the feeler l2! engages with the control button I43 of an electric push button switch 5. This switch is preferably of the type known as a micro switch, because of the characteristic of opening and closing upon minute displacements of the button I. This switch Ill is carried upon a bracket 1 beneath a cover ill on the stator S.

The switch I" is wired into a signal circuit, either audible or visible, or into the ignition cirare scraped by the rotor. Thus development of damaging trouble can be avoided.

In Fig. 8 is shown a scheme for inspecting the surface. of the armature 3|. This involves the provision of a hole l5l through the casing of the stator provided at its base with pipe threads I53 for a threaded plug I55 adapted to be operated from a wrench engaging extension I51. Thus the surface of the armature 3| may be inspected for scaling, eccentricity, or the like.

In view of the above, it will be seen that the several objects or the invention are achieved and other advantageous results attained.

As many changes could be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

I claim:

1. In apparatus of the class described, a magrespective belts being adjacent to opposite sides of the coil, said coil providing a toric flux field passing through the rotor and the stator and through said adjacent belts of poles, the poles in adjacent belts thereof being flared and staggered and overlapping peripherally within the coil.

5. In apparatus of the class described, a magnetic stator, a magnetic rotor within the stator, at least one annular coil carried by the stator, and a plurality of annular belts oi magnetic poles extending inwardly from said rotor toward the stator respectively located adjacent to opposite sides of the coil, said coil providing a toric flux field passing through the rotor and the stator and through said adjacent belts of poles, said poles being flared inwardly to assume an elongate shape axially, the ends of the teeth in one belt peripherally overlapping those in the other, but the end area of each pole being less than its area where it is connected to the stator.

netic stator, a magnetic rotor within the stator,

end members aflixed to the stator and forming a water-tight compartment around the rotor, at least one annular coil carried in the stator, annular means on the stator dividing said coil from any water in said compartment, and a plurality of annular belts of magnetic poles extending inwardly from said stator toward the rotor adjacent opposite sides of the coil, said coil providing a toric flux field passing through the rotor and the stator and through said adjacent belts of poles.

2. In apparatus of the class described, a magnetic stator member, a magnetic rotor member, at least one annular coil carried by one of said members, and a plurality of annular belts of magnetic poles extending radially from one of said members toward the other, respective belts being adjacent to opposite sides of the coil, said coil providing a toric flux field passing through the rotor and the stator and through said adjacent belts of poles, the poles in one belt being peripherally staggered with respect to those in the other, and being of elongate form substantially parallel to the axis of rotation, the adjacent ends of the elongate poles overlapping peripherally.

3. In apparatus of the class described, a magnetic stator member, a magnetic rotor member, at least one annular coil carried by one of said members, and a plurality of annular belts of magnetic poles extending radially from one of said members toward the other, respective belts being adjacent to opposite sides of the coil, said coil providing a toric flux field passing through the rotor and the stator and through said adjacent belts of poles, the poles in one belt being peripherally staggered with respect to those in the other, said poles being flared from their connections with their supporting member to assume an elongate shape parallel to the axis of rotation, the ends of the teeth in one belt peripherally overlapping those in the other but the end area of each pole being less than its area where connected to its supporting member.

4. In apparatus of the class described, a magnetic stator, a magnetic rotor within the stator, end members aflixed to the stator and forming a water-tight compartment around the rotor, at least one annular coil carried in the stator, annular means on the stator dividing said coil from water in said compartment, and a plurality of annular belts of magnetic poles extending inwardly from said rotor toward the stator, the

6. In apparatus of the class described, a magnetic stator, a magnetic rotor within the stator, end members afiixed to the stator and forming a water tight compartment around the rotor, at least one annular coil carried in the stator, separate annular band means on the stator dividing said coil from water in said compartment; and a plurality of annular rings forming belts of magnetic poles extending inwardly from said rotor toward the stator adjacent to opposite sides of the coil, said rings having water-tight connections with said band, said coil providing a toric flux field passing through the rotor and the stator and through said adjacent belts of poles, the poles in adjacent belts thereof being flared inwardly and staggered relatively and overlapping peripherally within said band.

'7. In apparatus of the class described, a magnetic stator, a magnetic rotor within the stator, end members affixed to the stator and forming a water-tight compartment around the rotor, at least one annular coil carried in the stator, separate annular band means on the stator dividing said coil from water in said compartment, and a plurality of annular rings forming belts of magnetic poles extending inwardly from said rotor toward the stator adjacent to opposite sides of the coil, said rings having water-tight connections with said band, said coil providing a toric flux field passing through the rotor and the stator and through said adjacent belts of poles, the poles in adjacent belts thereof being flared inwardly and staggered relatively and overlapping peripherally within said band, the end areas of the poles being less than their areas where they join their respective rings.

8. In apparatus of the class described, a magnetic stator, a magnetic rotor within the stator, end members aflixed to the stator and forming a water-tight compartment around the rotor, at least one annular coil carried in the stator, annular means on the stator dividing said coil from water in said compartment, and a plurality of annular belts of magnetic poles extending inwardly from said rotor toward the stator adjacent to opposite sides of the coil, said coil providing a toric flux field passing through the rotor and the stator and through said adjacent belts of poles, the poles in adjacent belts thereof being staggered, the poles of a given belt having axially protruding portions extending past the ends of the axially protruding portions of the poles in an adjacent belt. v

9., In apparatus. of the class described, a magnetic stator, a magnetic rotor within the stator, and members affixed to the stator and torming'a water-tight compartment around the rotor, at least one annular coil carried in the stator, annularmeans on the stator dividing said coil from water in said compartment, and a plurality of annular belts of magnetic poles extending inwardly from said rotor toward the stator adjacent to-opposite sides of the coil, said coil providing a toric flux field passing through the rotor and the stator and through said adjacent belts of poles, the poles in adjacent belts thereof being staggered, the poles of a given belt having axially protruding portions extending past the ends of the axially protruding portions of the poles in an adjacent belt, the waist area of each pole near where it joins the stator being substantially one and three-tenths times the axially extended rotor and the stator and passing through said teeth, and enclosures on the stator cooperating with the rotor and having water outlets, and means for introducing water into the space between the rotor and the stator at a plurality of points between said and members at a rate small enough to produce a rain of water in response to alternate contacts between the rotor and said teeth.

11. A dynamometer comprising a cylindric magnetic stator, a magnetic rotor within the stator, flux-concentrating teeth arranged in staggered peripheral belts and extending inwardly from the stator, the teeth in one belt peripherally overlapping teeth in an adjacent belt, a plurality of annular field coils carried in the stator and around the rotor and providing a toric flux field interlinking the rotor and the stator and passing through said teeth. and enclosures on the stator cooperating withthe rotor and having water outlets, and means for introducing water into the stator, a rotor within the stator having a smooth space between the rotor and the stator at a plu- 12. A dynamometer comprising a cylindric stator, a rotor within the stator having a smooth cylindric surface, peripherallyspaced teeth extending inwardly from the. stator, the ends of the teeth being in close proximity to the surface of the rotor, means for circulating water between the armature and the rotor and around said teeth, said teeth being axially longer than they are peripherally wide and tapering axially and also tapering down radially from their point of attachment with the stator and toward the rotor, and means generating a fiux field interlinking the stator and the rotor through said teeth.

13. A dynamometer comprising a cylindric stator, a rotor within the stator having a-srnooth cylindric .exterior surface, peripheral groups of teeth extending inwardly from the stator'toward the rotor, the teeth in each group being peripherally spaced and axially staggered with respect to the teeth, in the adjacent group and means providing a flux field interlinking the stator and the rotor through said adjacent groups of teeth so as to make one group of north polarity cylindric exterior surface, peripheral groups of teeth extending inwardly from waist connections with the stator toward the rotor, the teeth in each group being peripherally spaced and axially staggeredwith respect to the teeth in the adjacent group, means providing a flux field interlinking the stator and the rotor through said adjacent groups of teeth so as to make one group of north polarity and the other of south polarity, the groups of teeth being spaced from one another at their points of connection with the cylindric stator but flaring axially toward the rotor to an extent whereby they overlap peripherally.

15. A dynamometer comprising a cylindric stator, a rotor within the stator having a smooth cylindric exterior surface, peripheral groups of teeth extending inwardly from waist connections with the stator toward the rotor, the teeth in each group being peripherally spaced and axially staggered with respect to the teeth in the adjacent group, means providing a fiux field interlinking the stator and the rotor through said adjacent groups of teeth so as to make one group or north polarity and the other of south polarity, the groups of teeth being spaced from one another at their points of connection with the cylindric stator but flaring axially toward the rotor to an extent whereby they overlap peripherally, each tooth having an end area less than its waist area at said connection with the stator.

16. A dynamometer comprising a cylindric stator, a rotor within the stator having a smooth cylindric exterior surface, peripheral groups of teeth extending inwardly from waist connections with the stator toward the rotor, the teeth in each group being peripherally spaced and axially staggered with respect to the teeth in the adjacent group, and means providing a fiux field interlinking the stator and the rotor through said adjacent groups of teeth so as to make one group of north polarity and the other of south polarity, the groups of teeth being spaced from one another at their points of connection with the cylindric stator but flaring axially toward the rotor to an extent whereby they overlap peripherally, each of said teeth having their ends tapered axially and also having their sides tapered radially toward the rotor.

1'7. A dynamometer comprising a cylindric stator, a rotor within the stator having a smooth (ill cylindric exterior surface, peripheral groups of teeth extending inwardly from the stator toward the'rotor, the teeth in each group being peripherally spaced and axially staggered with respect to the teeth in the adjacent group, means providing a flux field interlinking the stator and the rotor through said adjacent groups of teeth so as to make one group'of north polarity and the other of south polarity, the groups of teeth being spaced from one another at their points of connection with the cylindric stator but flaring areas of said teeth where they spacedly connect with the cylindric portion of the stator having a greater area than the ends of the teeth adjacent to said rotor.

. 18. In a dynamometer, a stator comprising an outside cylindric body composed of adjacent rings of T-shaped cross sections providing peripheral spaces therebetween, peripheral electric coils between pairs of said rings, circular watertight bands of restrictive magnetic cross section joining said rings at said grooves and within the coil to provide substantially water-tight compartments for the coils, radial teeth extending inwardly from the rings and having bases of axial length-about equal to the ring widths, the teeth in a group attached to one ring being staggered with respect to the group of teeth attached to an adjacent ring, all of the teeth extending axially a length adapted to overlap endwise peripherally over the water-tight band.

19. In a dynamometer, a stator comprising an outside cylindric body composed of adjacent rings of T-shaped cross sections providing peripheral spaces therebetween, peripheral electric coils between pairs of said rings, circular watertight bands of limited cross section joining said rings at said grooves and within the coil provide substantially water tight compartments for the coils, radial teeth extending inwardly from the rings and having bases of axial length about equal to the ring width, the teeth in a group attached to one ring being staggered with the group of teeth in a' group attached to an adjacent ring, all of the teeth extending axially to a length adapted to overlap peripherally said water-tight ring lying under the overlapped portion, and means for introducing water through the rings between adjacent coils and around said teeth.

20. A dynamometer comprising a stator, a hollow rotor within the stator having a smooth cylindric surface, teeth extending from the stator toward the rotor, means generating a flux field interlinking the rotor and the stator through said teeth, endwise heads on the rotor, said rotor tapering in section toward said heads.

21. A dynamometer comprising a stator, a hollow rotor within the stator having a smooth cylindric surface, teeth extending from the stator toward the rotor, means generating a flux field interlinking the rotor and the stator through said teeth, a part of the rotor extending beyond the teeth, and endwise heads on the rotor, said rotor tapering in section toward said heads where it extends beyond said teeth.

22. A dynamometer comprising a stator, a hollow cylindric rotor, said stator having internal spaced teeth extending radially in toward the rotor, whereby water space is provided between the stator and the rotor around said teeth, said stator having substantially water-tight peripheral spaces, peripheral field coils in said spaces, said stator having openings for the introduction of water into said tooth space, end members on the stator enclosing said rotor, centrifugal catch means including openings through the rotor for directing water to the interior of the rotor, and said rotor having outlet means for return of water to the space between the rotor and stator.

23. A dynamometer comprising a stator, a hollow cylindric rotor, said stator having internal spaced teeth extending radially in toward the rotor whereby water space is provided between the stator and the rotor around said teeth, said stator having substantially water-tight peripheral spaces, peripheral field coils in said spaces, said stator having openings for the introduction of water into said tooth space, end members on the stator enclosing said rotor, centrifugal catch means including an opening in the rotor for directing water to the interior of, the rotor, and said rotor having outlet means spaced from said inlet means for return of water to the tooth space,

on its interior surface, said inlet and outlet openings providing circulating means for continuously changing said film.

24. A dynamometer comprising a stator, teeth thereon, a rotor therein, said stator having substantially water-tight separate peripheral pockets therein, peripheral field coils in said pockets, said stator at its bottom being provided with a drainage space connecting said pockets and leading to its exterior to drain off accidental leakage of water into said spaces, and means for circulating water between the rotor and the stator and around said teeth.

25. A dynamometer comprising a stator, a rotor therein, spaced flux concentrating teeth extending inwardly from the stator into close adjacency with the surface of the rotor, said stator having substantialy separate water-tight peripheral pockets therein, peripheral field coils in said pockets, said stator at its bottom being provided with a drainage space connecting pockets and leading to its exterior to drain off accidental leakage of water into said spaces, and means for circulating water between the rotor and the stator and around said teeth.

26. A dynamometer comprising a substantially cylindric stator, a hollow substantially cylindric rotor therein and havin a smooth exterior surface, spaced fiux concentrating teeth extending from the stator, the ends of which are closely adjacent to'the rotor, end members on the stator and enclosing the rotor, means generating flux interlinking the stator and the rotor through said teeth, means introducing water through the stator at several poins between said end members to pass toward said end members, said rotor having water inlet means at its ends and a water outlet at an intermediate point, centrifugal catch means are receiving some of the water that flows from between the rotor and the stator and for forcing it through said inlet means in the rotor to be centrifugally positioned in a sheet on the inner hollow surface of the rotor, excess water within the rotor flowing centrifugally through said intermediate outlet.

27. A dynamometer comprising a substantially cylindric stator, a hollow substantially cylindric rotor therein and having a smooth exterior surface, spaced flux concentrating teeth extending from the rotor toward the stator, the ends of said teeth being closely adjacent to the rotor, an end member on the stator and enclosing the rotor, means generating flux interlinking the stator and the rotor through said teeth, means introducing water radially through the stator at one point to flow toward said end member, said rotor having water inlet means at an end and wtaer outlet means at another point, centrifugal catch means are receiving some of the water that flows from between the rotor and the stator into the end member and for forcing it through said inlet means in the rotor to be centrifugally positioned in a sheet on the inner hollow surface of the rotor, excess water within the rotor flowing centrifugally through said outlet, the interior of the rotor being formed to maintain under centrifugal force a cylindric sheet of water on the interior of the rotor surface, whereby flow of water on the outside of the rotor is in one direction and the flow of water on the inside of the rotor is opposite.

28,-. A dynamometer comprising a, substantially cylindric stator, a hollow substantially cylindric rotor therein and having a' smooth exterior surface, spaced flux concentrating teeth extending from the rotor toward the stator, the ends of which teeth are closely adjacent to the rotor, end members on the stator and enclosing the rotor, means generating flux interlinking the stator and the rotor through said teeth, means introducing water radially through the stator at a point between said end members to flow toward said end members, said rotor having water inlet means at its ends and water outlet means at mid points, centrifugal catch means are receiving some of the water that ilows from between the rotor and the stator ino the end members and forcing it through said inlet means in the rotor to be centritugally positioned in a sheet on the inner hollow surface of the rotor, excess water within the rotor flowing centriiugally through said outlets therein to recirculate in the space between the stator and the rotor. the interior of the rotor bein: formed to maintain under centrifugal force a cylindric sheet of water on the interior of the ass-mac rotor surface, whereby now of water on the outside of the rotor is from its mid portions to its ends and the flow of water on the inside of the rotor is from its ends toward its mid portion, sump means at the bottoms of said end members and suction means (or eliminating water from the sump means.

29. In eddy-current apparatus, relatively rotary members, an annular coil, and a pair of annular belts of magnetic poles extending radially from one of said members toward the other, the respective belts being axially on opposite sides of the coil, said coi-l providing a toric i'lux iield passing through both of the relatively rotary members and through said annular belts of poles, the poles in one belt being peripherally staggered with respect to'those in the other and being of elongate torm substantially parallel to the axis of rotation, the adjacent ends of the elongate poles g0 overlapping peripherally.

MARTIN P. WINTHEB. 

